Machines used to wrap and seal articles and packages in thermoplastic film are well known in the art. Two types of machines are commonly referred to as side-sealing and lap-sealing machines. In the typical side-sealing configuration, an article or set of articles travels, typically via a conveyer belt, toward the machine. A sheet of center-folded plastic film, having two layers, is fed from a direction which is preferably perpendicular to the direction of the conveyer. The two layers of the film are then separated such that the article is placed between the lower layer and the upper layer. On one side of the article is the center-fold, while on the other side, there is an open edge where the two layers are not attached. The machine has a side sealing mechanism, which typically comprises several sets of belts to hold and guide the film, a heating/sealing element that fuses or welds the two free layers together and a cutting element that removes the excess material. Thus, as the article passes by the side sealing mechanism, this open edge is sealed by welding the two layers together, the plastic is cut and the waste is removed and discarded. At this point, the plastic film resembles a tube, with openings at both the leading and trailing ends of the article, but sealed along both sides. As the article continues to advance, an end sealing mechanism is then employed to seal the film at the leading end of the article. The article is further advanced and the end sealing mechanism then seals the film at the trailing end of the article.
The sealing and cutting performed by the side sealing unit can be done in a variety of ways. Some of these methods include hot air, hot knife, hot wire, band sealing and hot wheel. The first three approaches (hot air, hot knife and hot wire) accomplish the cutting and sealing processes without the use of pressure. In contrast, the band system compresses the film between two hot blocks and then a cut is made subsequent to the sealing process. Finally, the hot wheel system includes a heated wheel with a blade in the center that cuts the film.
In addition to high quality seals, the throughput of the system is also a concern. Many different types of sealing and cutting processes can be used, which perform well at low speeds, such as less than 40 feet per minute. However, at high speeds, such as 60 feet per minute, it becomes difficult to create good quality seals. This problem is exacerbated by thicker films, which require more heat to properly seal, and are obviously more difficult to cut through.
A side sealing machine that can operate at high speed and perform high quality seals, even on thick films, would be very beneficial. Such a machine would allow increased throughput and higher quality. In addition, a method of cutting and sealing a film which allows high quality seals and high throughput would be advantageous.